1. Field of the Invention
The present invention relates to a radiation sensitive composition (which will be referred to as "a resist composition" hereinafter) which is sensitive to radiation such as ultraviolet rays, deep ultraviolet rays, X-rays, and corpuscular beams such as electron beams and so on, and more particularly, to a resist composition which has high safety in use, good application, low film thickness loss at the time of development, uniformity in line width of pattern after development and good resist adhesion to substrate during development.
2. Description of the Related Art
In manufacturing an integrated circuit, a color filter, a liquid crystal display element and the like, a fine or minute manufacturing technique is required, to meet such requirement, a resist composition is conventionally utilized. As the resist composition there are conventionally known positive type and negative type. Both the resists are dissolved by solvent into solution. This resist composition is applied to a substrate such as a silicon substrate and a glass substrate by a known application method such as spin coating and roller coating, and is then prebaked to form a resist film. After that the resist film is exposed to ultraviolet rays, deep ultraviolet rays, X-rays or corpuscular beams such as electron and the like beams in accordance with the photosensitive wave range of a resist material to be used and is developed. After that, dry etching is performed if necessary and a desired resist pattern is formed. Various types of solvents are conventionally known as a solvent used for the above described resist composition, and a suitable solvent is selected and used in view of solubility, application, sensitivity, development property and characteristics of pattern to be formed. On the other hand, apart from properties such as resist forming characteristic and the like, many solvents have a problem in view of safety to human body. Recently attention to the safety to human body has especially been paid, and it is the fact that a solvent is selected in view of the safety. For example, ethylene glycol monoethyl ether acetate had been known as a solvent which was excellent in various properties such as solubility, application and resist forming characteristic. But after the problem of safety to human body was pointed out, ethylene glycol monoethyl ether acetate has not been used at all as a solvent for the resist composition. Alternatively, propylene glycol monomethyl ether acetate has mainly been used as a safe solvent. Other than propylene glycol monomethyl ether acetate, there are known safe solvents such as ethyl lactate and methyl-n-amyl ketone and the like. However, these solvents having high safety as compared with ethylene glycol monoethyl ether acetate have a problem that properties such as resist forming characteristic are not sufficient. For example, in the case of propylene glycol monomethyl ether acetate, when the resist composition is applied onto the substrate for forming a resist film, an amount of residual solvent in the film at the time of film formation are large, and there are problems such as that reduction rate of film thickness, uniformity of line width and adhesion of resist film at the time of development are deteriorated. Reasons for such deterioration are that although the propylene glycol monomethyl ether acetate itself is a solvent having high evaporation speed, if it is used as a solvent of the resist composition, evaporation only around the surface of the coating is took place and a so-called film is formed on the surface of the coating and thus solvent involved under the surface is prone not to evaporate. For this reason, a solvent having high safety and good resist forming characteristic at the same time is required.